1. Field of the Invention
The present invention is generally related to an anti-fouling apparatus for marine components and, more particularly, to a device that creates an electric current in the region proximate an underwater surface in order to inhibit the growth of marine life on an underwater surface such as a boat hull.
2. Description of the Prior Art
For over a thousand years, it has been known that a ship's hull is subject to fouling by marine growth. Copper cladding had been used successfully for many years until the introduction of vessels with iron hulls which prevented its use because of the potential for galvanic action. By 1850, various paints containing copper salts had been developed. Over the past few centuries, the pace of the development of anti-fouling techniques has been influenced by warfare, and several naval encounters have been decided by the greater speed of a naval vessel that resulted because of superior anti-fouling technology.
Currently, copper salts are used in the majority of anti-fouling paints, although the most effective modem anti-foulings contain tributyltin (TBT) as well as copper salts. Recent restrictions on the use of TBT and anti-fouling paints has led to renewed interest in developing novel, environmentally acceptable anti-fouling techniques.
Throughout the description of the present invention, the unwanted growth on a ship's hull or other underwater surface will be referred to as fouling. Although fouling is primarily a biological phenomenon, its implication relate to engineering Due to an increase in the resistance to movement of the hull through water, fouling of the hulls of ships results in a reduction in speed, an increase in the cost of fuel, and losses in both time and money in the application of remedial measures.
Underwater surfaces rapidly absorb organic material, referred to as conditioning films, which may influence the subsequent settlement of microorganisms. Bacteria and diatoms are soon present after immersion in water, resulting in a slime that covers the submerged surface. Following the establishment of the micro fouling slime layer, macro fouling rapidly develops. The macro fouling community is often described as either soft fouling or hard fouling. Soft fouling comprises algae and invertebrates such as soft corals, sponges, anemones, tunicates, and hydroids while hard fouling comprises invertebrates such as barnacles, mussels, and tubeworms.
Mariners from ancient times were aware of the problems resulting from both is boring and fouling organisms. Various treatments were employed, and some of these techniques have been retried many times in many forms over more than 2,000 years. The ancient Phoenicians and Carthaginians addressed this problem over 400 years BC. The Greeks and Romans both independently used lead sheathing which the Romans secured by copper nails. In the early 16th century, Spain officially adopted lead sheathing and its use soon spread to France and England. Although it actually offered little in the way of protection against fouling, lead was the material most frequently used prior to the eighteenth century. However, its corrosive effect on iron ships was soon noticed and the British Admiralty abandoned the use of lead in 1682 for that reason.
Other treatments to prevent worms from penetrating the planking relied on a wooden sheath placed over a layer of animal hair and tar. The wooden sheathing was sometimes filled with iron or cooper nails that had large heads. This, in effect, created an outer metallic cladding. Paints were also used that had mixtures of tar, brimstone and grease. The first successful anti-fouling device was copper sheathing and the first documented evidence for the use of copper as an anti-fouling method dates back to 1625. Copper was used in 1758 on the hull of the HMS Alarm, and by 1780 copper was in general use by the British Navy. Sir Humphry Davy showed that it was actually the dissolution of the copper in sea water that prevented fouling.
In the nineteenth century, with the growing importance of iron ship building, the use of copper sheathing on the boats was discontinued. As a result, the weight of fouling quickly made the ships unmaneuverable and unseaworthy. Various alternatives were tried including sheathings of zinc, lead, nickel, galvanized iron and alloys of antimony, zinc and tin, followed by wooden sheathing which was then layered with copper.
By 1960, metallic soap was applied hot and contained copper sulfate. From these early attempts at coatings, anti-fouling paints incorporating cuprous oxide, mercuric oxide, or arsenic in shellac varnish or a resin matrix with turpentine, naphtha or benzene as solvents developed. From these formulations, modern anti-fouling paints were developed. Anti-fouling paints are currently in wide use on yachts and pleasure crafts as well as deep sea vehicles. The presence of tributyltin (TBT) in estuaries and in the sea is thought to result from the increased use of tributyltin-containing paints on these types of vessels.
Another technique for inhibiting fouling is to reduce the ease with which bacteria and algae adhere to the surfaces. The main type of low energy non-biocidal coatings are fluoro-polymers and silicones. Fluoropolymers have been under development in the United States during the past several decades. They are based on fluoro-polyurethane paints, either pigmented with PTFE or containing silicone for fluoro-epoxy additives. Although the surfaces do accumulate fouling organisms, their attachment is weak. Coatings developed to date require twice yearly cleaning with bristled brushes to remove fouling growth and can therefore only be useful as coatings on small boats.
Various other non-toxic techniques have been attempted. Both ultrasonic (e.g. 14 kHz) and low frequency (e.g. 30 Hz) sound waves inhibit barnacle settlement and may have application to fouling control in certain circumstances. These and many other anti-fouling techniques are described in an article written by Maureen Callow in the publication titled "Chemistry and Industry" at Section 5, pg. 123, on Mar. 5, 1990.
As described in the Baltimore Business Journal, Vol. 10, No. 47, Section 1, pg. 3 on Apr. 23, 1993, McCormick & Company has discovered that its red pepper extracts are natural repellents of barnacles and zebra mussels. A coating of this type has been tested, and it has been determined that it repels both barnacles and zebra mussels which have become costly nuisances in the Great Lake Region by clogging intake pipes for power plants and water treatment plants. It is estimated that several billion dollars in damage will be caused by zebra mussels before the turn of the century.
U.S. Pat. No. 5,532,980, which issued to Zarate, et. al. on Jul. 2, 1996, discloses a vibrational anti-fouling system. The system produces vibrations in an underwater structure for the purpose of inhibiting the attachment of aquatic life forms to the structure. The system includes a controller which drives one or more transducers. The transducer comprises a housing, one end of which i s closed by a resilient diaphragm. An electromagnet with soft magnetic core is contained in the housing spaced from the unsupported portion of the diaphragm. The unsupported portion of the diaphragm is mounted over an underwater structure. In operation, the electromagnet is excited with a current pulse, which deforms the diaphragm so that the housing moves towards the structure. As the current drops off, the diaphragm is restored to its original shape and the housing moves away from the structure imparting a vibrational force to the structure. The transducer includes an elastic membrane to compensate the changes in temperature and pressure commonly found when working underwater. The magnetic cores positioned in the transducers are saturated by current pulses generated by the controller to eliminate the effects of component variations and allow multiple units to be connected to the controller without changes in sound levels. The system is highly resistant to electrolytic corrosion since, most of the time, there is no voltage difference between the resonators, wires and ground.
U.S. Pat. 5,386,397, which issued to Urroz on Jan. 31, 1995, describes a method and apparatus for keeping a body surface, which is in contact with water, free of fouling. A sound wave is generated for keeping a surface free of scale, fouling and dirt by the adherence of organisms such as marine life, the surface being part of the body that is in contact with water. The method comprising of steps of generating and emitting from at least one location of the body, at least one high frequency sound wave train forming, adjacent to the body surface, a vibrating field encircling the body surface. The molecular energy of the water within the field is increased to generate a drastic drop in the density of the water as well as the density of the cells of the organisms entering the vibrating field. This alters the habitat of the organisms and discourages the organisms from adhering to the body surface.
U.S. Pat. 4,058,075, which issued to Piper on Nov. 15, 1977, discloses a marine life growth inhibitor device. The device is used for inhibiting marine life on the outer surface of submerged object such as boat. The device includes a controller connected to a source of electrical power and a plurality of speakers electrically connected to the controller and attached at predetermined locations on the interior of the boat's hull, whereby vibrations may be transmitted through the hull. The controller may also include a transformer for reducing the voltage of the alternating current power source. Each of the plurality of speakers has a speaker diaphragm having first and second speaker diaphragm sides. Each of the speakers is mounted in a speaker housing secured to the hull of the boat for enabling transfer of acoustical energy from both the first and second side of the speaker diagram to the boat hull to inhibit the growth of marine life on the exterior surface of the boat hull. The speakers are selected to produce acoustical vibration in the audible range.
U.S. Pat. No. 5,143,011, which issued to Rabbette on Sep. 1, 1992, discloses a method and apparatus for inhibiting barnacle growth on boats. The system for inhibiting growth of barnacles and other marine life on the hull of a boat includes a plurality of transducers or vibrators mounted on the hull and alternately energized at a frequency of 25 Hertz through a power source preferably the boat battery, and a control system. The system has two selectable operating modes. One is continuous and the other is periodic. Also, when the voltage of the battery falls below a predetermined level, transducers are automatically deenergized to allow charging of the battery after which the transducers are energized.
U.S. Pat. No. 5,629,045, which issued to Veech on May. 13, 1997, describes a biodegradable nosiogenic agents for control of non-vertebrae pests. Fouling of marine structures, such as boats, by shell bearing sea animals which attach themselves to such structures, such as barnacles, is generally inhibited by coatings containing lipid soluble, non-toxic, biodegradable substances which prevent the animals from sitting down on the structures. These substances attack the nervous system of the barnacle, neutralize the glue extruded by the barnacle, and otherwise prevent the barnacles from attaching themselves to surfaces immersed in the aqueous marine environment while being benign to the environment. A preferred inhibitor is pepper containing capsaicin. The inhibitor is incorporated into standard marine paints, impregnates, varnishes and the like.
U.S. Pat. No. 5,318,814, which issued to Elliott et al on Jun. 7, 1994, describes the inhibiting of the settling of barnacles. Settlement of barnacles on surfaces in a marine environment is inhibited by employing as a construction material for said surfaces of polymers including methyl methacrylate and an effective amount (preferably about 2% to about 10%) of a copolymerizable N-substituted maleimide.
U.S. Pat. No. 4,012,503, which issued to Freiman on Mar. 15, 1977, discloses a coating composition used to control barnacles. Toxicant compositions containing the combination of tri-n-butyltin fluoride with zinc oxide and specified substituted triazines effectively inhibit the development of marine organisms, including barnacles and algae, that are responsible for fouling. These compositions are particularly useful as the active component in antifouling coatings.
U.S. Pat. No. 4,214,909, which issued to Mawatari et al on Jul. 29, 1980, describes an aquatic antifouling method. The method for controlling fouling to structures caused by aquatic fouling organisms such as barnacles, slime, sea moss, algae, etc. which comprises applying to the structures sesquiterpene alcohols such as farnesol, nerolidol, and dehydronerolidol, and the organic carboxylic acid esters thereof.
U.S. Pat. No. 5,465,676, which issued to Falcaro on Nov. 14, 1995, discloses a barnacle shield. A system for discouraging and inhibiting marine growth onto a boat's underwater hull surface comprises a plurality of sections of foam filled PVC pipe tied together to form a flotation frame, an envelope of flexible, polyethylene, bubble wrap material, of a size and shape to enclose the underwater part of a boat's hull, and affixed to and supported by the flotation frame, a sprinkler hose affixed to the flotation frame for injecting fresh water for washing the boat's underwater hull, and a plurality of drain/check valves mounted in the envelope for eliminating the wash down water in the envelope.
U.S. Pat. No. 4,170,185, which issued to Murphy et al on Oct. 9, 1979, describes a means for preventing marine fouling. The effective antifouling result with respect to marine creatures such as barnacles is achieved by energizing a piezofilm layer carried on the outside of a vessel to cause mechanical vibration of the layer.
U.S. Pat. No. 4,046,094, which issued to Preiser et al on Sep. 6, 1977, discloses an antifouling system for active ships which are at rest. A system for discouraging and inhibiting growth of the entire marine fouling community onto a ship hull while it is at rest in brackish or seawater is described. A pipe or pipes having nozzles distributed therealong, run the length of the keel. Fresh water is supplied to the pipe which flows out the nozzles and up along the hull to create and maintain a moving boundary layer of fresh water. Such movement also serves to inhibit fouling. An enclosure comprising segmented, over-lapping opaque curtains hang down by weights, from the ship-deck. These curtains serve to prevent light from reaching the hull, and to protect the thin boundary layer of fresh water from the disruptive, mixing actions caused by the surrounding currents. Thus the marine fouling community, including tubeworms, barnacles, grass, and algae, may be inhibited from growing and adhering to the hull surface.
U.S. Pat. No. 4,283,461, which issued to Wooden et al on Aug. 11, 1981, describes a piezoelectric polymer antifouling coating. An antifouling coating for marine structures in the form of a film containing piezoelectric polymer material, which, when electrically activated vibrates at a selected frequency to present a surface interfacing with water which is inhospitable for attachment of vegetable and animal life including free-swimming organisms thereby discouraging their attachment and their subsequent growth thereon to the macrofoulant adult stage is disclosed.
U.S. Pat. No. 5,342,228, which issued to Magee et al on Aug. 30, 1994, discloses a marine drive which is provided with a large volume anode, about 30 cubic inches, for galvanic protection. The anode is a brick-like block member tapered along each of its height, width, and length dimensions. The drive housing has a anode mounting section extending rearwardly therefrom and has a downwardly opening cavity of substantially the same shape and volume as the anode, and receiving the anode in nested flush relation.
U.S. Pat. No. 5,716,248, which issued to Nakamura on Feb. 10, 1998, discloses a sacrificial anode for a marine propulsion unit. The sacrificial anode arrangements for a marine propulsion unit is disclosed wherein the sacrificial anode is juxtaposed to the trim tab and is detachably connected to the lower unit housing by fastening means which can be removed from the upper surface thereof. In one embodiment, the trim tab is detachably connected to the sacrificial anode and is connected to the outer housing portion through the sacrificial anode.
U.S. Pat. No. 5,298,794, which issued to Kuragaki on Mar. 29, 1994, describes an electrical anticorrosion device for a marine propulsion apparatus. The device primarily relates to an electrical anticorrosion apparatus for a marine propulsion arrangement. More particularly, the device relates to an anodic protection arrangement which is suitable for use with an inboard/outboard propulsion unit. According to the description in this patent, an anode and the reference electrode are housed within a housing unit which is mounted upon a propulsion unit mounting bracket. The two electrodes are arranged so that each is essentially equidistant from a point located approximate midway across the lateral width of an outboard drive unit, which unit is secured to the mounting bracket, when the unit is positioned for driving the associated watercraft in a generally forward direction.
U.S. Pat. No. 4,322,633, which issued to Staerzl on Mar. 30, 1982, discloses a marine cathodic protection system. The system maintains a submerged portion of the marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a pre-selected constant potential in response to the sensed potential at a closely located reference electrode during operation. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.
U.S. Pat. No. 5,052,962, which issued to Clark on Oct. 1, 1991, describes a naval electrochemical corrosion reducing. The corrosion reducer is used with ships having a hull, a propeller mounted on a propeller shaft and extending through the hull, therein supporting the shaft, at least one thrust bearing and one seal. Improvement includes a current collector and a current reduction assembly for reducing the voltage between the hull and shaft in order to reduce corrosion due to electrolytic action. The current reduction assembly includes an electrical contact, the current collector, and the hull. The current reduction assembly further includes a device for sensing and measuring the voltage between the hull and the shaft and a device for applying a reverse voltage between the hull and the shaft so that the resulting voltage differential is from 0 to 0.05 volts. The current reduction assembly further includes a differential amplifier having a voltage differential between the hull and the shaft. The current reduction assembly further includes an amplifier and the power output circuit receiving signals from the differential amplifier and being supplied by at least one current supply. The current selector includes a brush assembly in contact with a slip ring over the shaft so that its potential may be applied to the differential amplifier.
U.S. Pat. No. 4,559,017, which issued to Cavil et al on Dec. 17, 1985, discloses a constant voltage anode system. The marine propulsion unit has a housing exposed to sea water and subject to attack by the sea water. It has a permanent type anode housing with a substantially constant surface characteristic which is mounted on the housing and supplied with constant voltage. Holes under the anode through the housing which extend to interior passages permits the current of the anode to influence and protect the passages.
The patents described above are hereby explicitly incorporated by reference in the following description.
Over the previous thousand years that mankind has ventured across the seas in ships, many attempts have been made to avoid the disastrous effects of marine fouling on the hulls of those ships. These attempts have included various types of cladding, treating, and painting. In addition, electromechanical schemes have been used to vibrate the hulls for the purpose of discouraging the attachment of various types of micro-organisms. Fresh water has been used to discourage the growth of barnacles and other marine life.
As described above, fouling of underwater surfaces has been recognized as a problem for many years. Anti-fouling techniques, such as biocidal paints, can contribute to the pollution of waterways. Many other methods simply are not effective. It would therefore be significantly beneficial if a device or method could be developed which does not pollute the environment, but effectively inhibits the growth of marine organisms on surfaces which are submerged in water such as boat hulls, pipes, pilings, and grates.